Environment variables in Linux CLI - Step-by-Step Execution

Concept Flow - Environment variables

Start shell session

↓

Set environment variable

↓

Use variable in commands

↓

Variable accessed by shell or programs

↓

End session or export variable for child processes

This flow shows how environment variables are set, used, and accessed in a shell session.

Execution Sample

Linux CLI

MY_VAR=hello
export MY_VAR
echo $MY_VAR

Sets an environment variable MY_VAR to 'hello', exports it, then prints its value.

Execution Table

Step	Command	Action	Variable State	Output
1	MY_VAR=hello	Assign MY_VAR locally	MY_VAR=hello (local)
2	export MY_VAR	Make MY_VAR available to child processes	MY_VAR=hello (exported)
3	echo $MY_VAR	Print value of MY_VAR	MY_VAR=hello (exported)	hello
4	exit	End shell session	Session ends

💡 Shell session ends, environment variables cleared unless saved in config files

Variable Tracker

Variable	Start	After Step 1	After Step 2	After Step 3	Final
MY_VAR	undefined	hello (local)	hello (exported)	hello (exported)	session ends

Key Moments - 2 Insights

Why does MY_VAR need to be exported to be available to child processes?

Because local variables are only visible in the current shell. Exporting MY_VAR (see step 2 in execution_table) makes it part of the environment passed to child processes.

What happens if you try to echo $MY_VAR before setting it?

The output will be empty because MY_VAR is undefined. This is shown by the variable state 'undefined' before step 1.

Visual Quiz - 3 Questions

Look at the execution_table at step 3. What is the output of 'echo $MY_VAR'?

A hello

B $MY_VAR

C undefined

D error

💡 Hint

Check the Output column at step 3 in the execution_table.

At which step does MY_VAR become available to child processes?

A Step 3

B Step 1

C Step 2

D Step 4

💡 Hint

Look at the Variable State column and the Action column in the execution_table.

If you remove the 'export' command, what will be the output of 'echo $MY_VAR' in a child process?

A hello

B empty string

C error message

D $MY_VAR

💡 Hint

Refer to the key_moments explanation about exporting variables.

Concept Snapshot

Environment variables store data for shell and programs.
Set with VAR=value, export with 'export VAR' to share with child processes.
Access with $VAR.
Local variables are not passed to child processes.
Exported variables are inherited by child processes.

Full Transcript

Environment variables are named values stored in the shell environment. You can set a variable by typing VAR=value. This variable is local to the current shell session. To make it available to programs or child shells, you must export it using 'export VAR'. Once exported, the variable is passed down to child processes. You can access the value by prefixing the variable name with a dollar sign, like $VAR. If you try to use a variable before setting it, it will be empty. When the shell session ends, the environment variables are cleared unless saved in configuration files.